How to make my mp3 to m4a

hi i formated my pc recently and when i hit save this program used to convert my mp3 to m4a now it wont convert to m4a. Do i have to do something in the settings? (sorry for potato english its not my first language)

mp3tag does not deal with audio content, you'll need another program.

for converting files you can use ffmpeg, commandline:
"C:\Program Files\ffmpeg_static\bin\ffmpeg.exe" -i "MyFile.mp3" -y "MyFile.mp4"
(will automaticly select mp4a encoder when input file is audio only)

If you prefer using an UI, for example Mediapurge can do same from UI:
Select Convert files -> Select directory/files -> Next -> Select/Type Outputformat mp4 -> Next -> Finished!